对@ 的作用不是很清晰，学习了一下，站在巨人的肩膀上总结如下：

1.忽略转义字符

例如

string fileName = "D:\\文本文件\\text.txt";

使用@后

string fileName = @"D:\文本文件\text.txt";

2.让字符串跨行

例如

string strSQL = "SELECT * FROM HumanResources.Employee AS e"
   + " INNER JOIN Person.Contact AS c"
   + " ON e.ContactID = c.ContactID"
   + " ORDER BY c.LastName";

使用@后

string strSQL = @"SELECT * FROM HumanResources.Employee AS e
INNER JOIN Person.Contact AS c
ON e.ContactID = c.ContactID
ORDER BY c.LastName";

3.在标识符中的用法

C#是不允许关键字作为标识符(类名、变量名、方法名、表空间名等)使用的，但如果加上@之后就可以了
例如

public static void @static(int @int)
{
     if (@int > 0)
     {
         System.Console.WriteLine("Positive Integer");
     }
     else if (@int == 0)
     {
         System.Console.WriteLine("Zero");
     }
     else
     {
         System.Console.WriteLine("Negative Integer");
     }
}

4.在SQL T-CODE中的用法

comStr = $@"SELECT vrs.*, BinToDefect.XML_BinCode,BinToDefect.XML_Defect_Name, BinToDefect.Result, aos.Rework_Status 
         FROM ( SELECT * FROM [CustomDB].[dbo].[Orbo_VRS_Data] 
         WHERE ID > '{startId.ToString()}' 
         AND DateEnterMES BETWEEN @startTime AND @endTime 
         AND LotNO_MES='605000228877' 
         AND Classify !='' 
         AND BC_2DID !='' AND BC_2DID !='0' AND BC_2DID !='-1' 
         AND Unit_ID !='' AND Unit_ID !='0' AND Unit_ID !='-1' 
         AND Array_ID !='' AND Array_ID !='0' AND Array_ID !='-1' ) as vrs 
         LEFT join [CustomDB].[dbo].[Orbo_AOS_Data] as aos 
         ON vrs.BC_2DID=aos.BC_2DID 
         AND vrs.Array_ID = aos.Array_ID 
         AND vrs.Unit_ID = aos.Unit_ID 
         AND vrs.x = aos.x 
         AND vrs.y = aos.y 
         LEFT join [CustomDB].[dbo].[MES_DefectToBinCode] as BinToDefect 
         ON BinToDefect.Classify = vrs.Classify AND BinToDefect.Station='VRS' 
         ORDER BY vrs.BC_2DID,vrs.Layer_Name,vrs.Array_ID,vrs.Unit_ID,vrs.x,vrs.y";